1. Field of the Invention
This invention relates to the cogeneration of space/water heat and electrical power.
2. Background Information
In most regions of North America, space heating of buildings is a necessity for some portion of the year to maintain thermal comfort. Buildings are space-heated in a variety of ways, with one of the most common being forced warm air heating, using a blower to move the air over a centrally located heat exchanger. The majority of such heat exchangers are warmed directly by using the hot gases produced by a fossil fuel burner.
Buildings also require a source of electric power. Forced warm air space heating systems are in themselves a significant user of electric power. This electric power is normally provided by an electric utility through the local electric grid, with the generation of the electric power occurring at large power stations remotely located from the building. All forms of electric power generation at large remotely located generating plants result in a large fraction of the fuel energy being normally dissipated as waste heat. The combination of electric power generation with useful application of the heat energy that is inevitably produced during electric power generation is generally termed “cogeneration.” Cogeneration is the simultaneous production of useful electric power and heat from the same fuel and fuel burner.
Small-scale cogeneration of heat and electric power from fossil fuels to meet the on-site energy needs of residential and commercial buildings represents a major opportunity for reduction of energy costs and pollutant emissions, including CO2 greenhouse gas. There is a general trend in the regulatory management of energy resources to specifically allow and encourage the tie-in of small-scale cogeneration and renewable energy systems into the existing electric utility grid. This benefits the power generating authorities by allowing them to delay construction of new capacity. However, there is as yet no widespread use of small-scale cogeneration. The technical and economic inadequacies of existing small-scale cogeneration technologies, as well as historical energy supply and regulatory practices, have perpetuated this situation. A number of small-scale power generation technologies are emerging that may be used in such small-scale combined heat and power systems. These include internal combustion engines, Stirling engines, fuel cells, and steam engines. Small-scale combined heat and power systems are now commonly referred to as micro-combined heat and power systems or, more briefly, “micro-CHP” systems and will be referred to as such in this discussion for convenience.
To date, little attention has been paid to specifically how such small-scale power generation technologies would be practically integrated into central forced warm air heating furnaces and systems. Warm air is by far the most common type of space heating system used in residential buildings in North America. Also, nearly all candidate generator technologies suitable for use in small-scale cogeneration of electric power and heat incorporate a liquid cooling (for example, glycol, water, and mixtures thereof) circuit and are not practically or conveniently implemented with direct air cooling of the key function components. A small scale cogeneration design that is a simple additive combination of warm air heating units of conventional design with available liquid cooled electric power generation devices is neither mechanically or electrically practical and will lead to inefficient and expensive systems. An integrated system design as described herein that addresses the combined and complementary mechanical, thermal, electrical power, and control characteristics of all system components is essential to practical realization of warm air heating systems with cogeneration capability.
Many prior art cogeneration systems are targeted toward large-scale facilities, with designs that do not scale-down to a residential/small commercial application. They may involve the use of gas turbines and steam plants that cannot be reproduced for a residence. While attempts to produce a small-scale cogeneration system have been made, these either do not interface with commonly used warm air-handling systems, or are impractical to employ in a “real-world” application.
Taken individually or as a whole, the prior art fails to provide an overall design for a practically implemented forced fossil-fueled warm air heating system of modem features combined with an efficient, fossil-fueled electric generator with liquid heating capability with such combination system of providing space heating for thermal comfort while simultaneously maximizing the operation of the electric generator for the cogeneration of heat and electric power and providing the important additional functionality of emergency power supply. Hence, a practical, up-to-date and efficient small-scale cogeneration system, that is particularly suitable for use as a modern forced warm air heating system employed in many homes and enterprises, is highly desirable.